In the manufacturer of various semiconductor devices, wire bonding techniques are often used to connect components in the devices. For example, wire bonds (or wire loops) are often used to provide interconnection between a semiconductor die and contacts on a leadframe. An exemplary conventional wire bonding operation involves (1) bonding a free air ball to a first bonding location on a die (e.g., using ball bonding) to form a first bond, (2) extending a wire from the first bond toward a second bonding location on a leadframe, (3) bonding the end of the extended wire to the second bonding location to form a second bond, and (4) cutting the wire. In such a ball bonding operation, an electronic flame off (i.e., EFO) wand/electrode or the like is typically used to form the free air ball at the end of the wire at step (1).
Often, gold wire (which is substantially non-reactive with oxygen) is used in wire bonding processes; however, in certain applications, more reactive metals (e.g., copper, silver, palladium, aluminum, etc.) are used. These more reactive metals may react, for example, in the presence of oxygen and form oxides/oxidation on the wires (and/or wire ends or tails) which are undesirable for wire bonding.
In view of such potential oxidation, certain wire bonding systems include subsystems for providing a cover gas to the end of a wire during formation of the free air ball by the EFO wand. For example, U.S. Pat. No. 6,234,376, which is incorporated by reference in its entirety, discloses such a system.
Additionally, various subsystems of wire bonding machines are used to provide the cover gas to the bond site area of the wire bonding machine to reduce the potential for oxidation of the bonding wire in the bond site area. Exemplary subsystems for providing a cover gas in the bond site area include U.S. Patent Application Publication Nos. 2007/0284421; 2007/0251980; and U.S. Pat. Nos. 5,265,788; 5,395,037; 6,866,182; and 7,182,793.
It would be desirable to provide improved structures for reducing oxidation in wire bonding.